Silver halide photographic emulsions containing a blue black toner



Patented June 27, 1950 SILVER HALIDE PHOTOGRAPHIO EMUL SIONS CONTAINING A BLUE BLACK TONER John David Kendall and Douglas James Fry, Ilford, England, assignors 'to vIlford Limited, Ilford, England, a British company 3 j No Drawing. Application August 113.1947, Serial No. 768,498. In Great Britain August 20,- 1946 1 6 Claims. (Cl. 9 6) This invention relates to silver halide photographic emulsions and particularly to gelatino silver chloride photographic emulsions such as are used in development papers for contact printing, i. e. the so-called gaslight printing papers.

It is well known that the colour of developed images obtained from gelatino silver chloride development emulsions can be controlled to some extent by the addition of certain substances to the emulsion or to the developer. In the absence of any special additions the developed images may vary from a greenish to a fairly neutral black. It is generally preferred that the developed images should be on the bluer side of neutral black rather than on the greener side, and various suggestions have hitherto been made for obtaining the desired blue-black images. Thus it is known to include in the emulsion a small quantity of a quinine salt, which has the effect of yielding developed images of a good blue-black colour. Many compounds have been sug ested as developer additions for the same purpose, but from both manufacturers and users standpoints, it is better to include the blue-black toning substance in the emulsion during its manufacture since, the products can then be developed with standard developers.

According to the present invention silver chloride emulsions which yield images of excellent blue-black colour on development are obtained by including in the emulsion, not later than the stage at which the emulsion is developed and preferably during its manufacture, a 3-alkyl isoquinoline or a mineral acid salt of such compound.

The compound B-methyl isoquinoline and its homologues can be prepared from orthocyan benzyl cyanide and an appropriate fatty acid anhydride (Gabriel and Neumann, Berichte, 25,

3563). Examples of such compounds which can be used according to this invention are:

3-methyl isoquinoline, M. pt 68 C. 3-ethyl isoquinoline, B. pt 256 C. 3-propyl isoquinoline, B. pt 271 C. 3-isopropyl isoquinoline, B. pt 266 C. B-isobutyl isoquinoline, B. pt 278 C.

Analogous compounds in which the benzene ring is substituted, e. g. by hydrocarbon, alkoxy, hydroxy, halogen, nitro or amino, may also be employed.

As indicated above, the compounds can be used either as the free bases or as mineral acid salts. Thus, for example, the compounds may be used as the hydrochlorides or bisulphates.

The proportion of compound added to the used and on the precise nature of the emulsion. In general a good blue-black tone can be obtained using the compounds of this invention in proportions of the order of 25 cos. of a 1% solution of the compound per pound of liquid emulsion ready for coating, though lower proportions or higher proprtions can be used, e. g. of the order of 5 to cos. of a 1% solution per pound of emulsion. Smaller quantities of proportionately stronger solutions may be used if desired.

Many substances when added to photographic emulsions have undesirable effects on the qualities of an emulsion, i. e. loss of speed, increased tendency to the formation of fog (i. e. developed silver not arising from the exposure) and on the contrast of the developed images. It is a particular merit of the compounds used as blue-black toners according to the present invention that they do not have any serious adverse effect in respect of any of these properties.

The following example illustrates the invention:

Example A gelatino silver chloride emulsion of the gaslight type was prepared and to a portion of it was added 3-methyl isoquinoline at the rate of 5 cos. of a 5% solution of the compound in ethyl alcohol per pound of emulsion. A control sample containing quinine bisulphate as the blue-black toning agent was also prepared. The samples were coated on paper base, exposed, developed in a standard metol-hydroquinone developer, and the photographic properties of the images obtained were studied.

It was found that the added compound was as effective as quinine bisulphate in imparting a blue-black tone to the developed image, and that the compound had no appreciable effect on the other properties of the emulsion.

It is to be understood that in the foregoing description and in the following claims the expression silver chloride photographic emulsion means a photographic emulsion in which the predominant silver salt is silver chloride and includes the possibility of a small proportion of other silver halide being present. The binding agent for the silver chloride may be gelatin or any water-permeable synthetic resin or polymer, e. g. polyvinyl alcohol, polyvinyl acetals, synthetic linear polyamides, and the like.

What we claim is:

1. A silver chloride photographic emulsion containing a compound selected from the class con- 3 sisting of 3-alkyl isoquinolines and strong mineral acid salts thereof.

2. A gelatino silver chloride photographic emulsion containing 3-methyl isoquinoline.

3. A gelatino silver chloride photographic emulsion containing a strong mineral acid salt of 3-methyl isoquinoline.

4. A gelatino silver chloride emulsion containing a compound selected from the class consisting of 3-alkyl isoquinolines andstrong mineral acid salts thereof in a proportion of 0.5 to 0.05 gm. per pound of emulsion.

5. A photographic element comprising a support and a layer of a gelatino silver chloride photographic emulsion containing a compound selected from the class consisting of 3-alkyl isoquinolines and strong mineral acid salts thereof.

6. A photographic element comprising a paper support and a layer of a gelatino silver chloride 4 photographic emulsion containing a compound selected from the class consisting of 3-alky1 isoquinolines and strong mineral acid salts thereof.

JOHN DAVID KENDALL. DOUGLAS JAMES FRY.

REFERENCES CITED The following references are of record in th file ofv this patent:

UNITED STATES PATENTS Number Name Date 2,124,159 Weyde July 19, 1938 2,334,864 Carroll et a1 Nov. 23, 1943 2,398,778 Carroll et a1 Apr. 23, 1946 OTHER REFERENCES Handbook of Photography Henney and Dudley (1939) 'McGraw Hill 00., pp. cited p. 326, p. 345. 

4. A GELATINO SILVER CHLORIDE EMULSION CONTAINING A COMPOUND SELECTED FROM THE CLASS CONSISTING OF 3-ALKYL ISOQUINOLINES AND STRONG MINERAL ACID SALTS THEREOF INA PROPORTION OF 0.5 TO 0.05 GM. PER POUND OF EMULSION. 